Number Of String Word Frequency In A Sentence Using C#

using System;
class frequencyword {
    public static void Main() {
        string s1;
        Console.WriteLine("Enter the String : ");
        s1 = Console.ReadLine();
        Console.WriteLine(counting.CountStrFrequency(s1, "test"));
        Console.ReadKey();
    }
}
public static class counting {
    public static int CountStrFrequency(string text, string pattern) {
        int count = 0;
        int i = 0;
        while ((i = text.IndexOf(pattern, i)) != -1) {
            i += pattern.Length;
            count++;
        }
        return count;
    }
}